U.N. Agency to Say It Overstated Extent of H.I.V. Cases by Millions

By DONALD G. McNEIL Jr.

Published: November 20, 2007

CORRECTION APPENDED

The United Nations' AIDS-fighting agency plans to issue a report today acknowledging that it overestimated the size of the epidemic and that new infections with the deadly virus have been dropping each year since they peaked in the late 1990s.

The agency, Unaids, will lower the number of people it believes are infected worldwide, to 33.2 million from the 39.5 million it estimated late last year.

The statistical changes reflect more accurate surveys, particularly in India and some populous African countries. Some epidemiologists have criticized for years the way estimates were made, and new surveys of thousands of households in several countries have borne them out.

In only a few countries, such as Kenya and Zimbabwe, do the figures reflect widespread behavioral changes, such as decisions by many people to have sex with fewer partners.

Excerpts from the report were given to the news media in advance for release this evening, but an embargo on it was broken by other news organizations. Despite the revised estimates, the epidemic remains one of the great scourges of mankind. This week's analysis predicts that 2.1 million people died of AIDS in the last year, and 2.5 million were newly infected -- or about 6,800 every day.

The agency now believes that the number of new infections each year with H.I.V., the virus that causes AIDS, probably peaked in the late 1990s, or by 2001, at about 3 million.

Although new infections have dropped, the number of people with the disease is growing because more people infected with H.I.V. are living longer, thanks to antiretroviral drugs. With the world's population growing, the agency believes that the percentage of adults who are now infected remains roughly constant, at about 0.8 percent.

''This is not a surprise,'' said Daniel Halperin, an expert on H.I.V. infection rates at the Harvard School of Public Health and co-author of an article published three years ago arguing that estimates of infection rates were too high. ''The writing was on the wall years ago,'' he said.

''But,'' he added, ''this doesn't mean the epidemic is going away, everything is fine and now forget about it -- not at all. There are still about 10 countries in southern Africa that are real nightmares.''

In the past, global health officials have treated the epidemic as a cyclone spiraling ever upward with no end to new infections in sight.

But better surveys, particularly a household survey in India, have driven the figures down.

Until recently, most national estimates were made by giving anonymous blood tests to some young women who came into public health clinics because they were pregnant or feared they had a sexually transmitted disease; those results were expanded with statistical models.

But epidemiologists have realized that such a method -- usually applied in big urban clinics because it was more efficient -- oversampled prostitutes, drug abusers and people with multiple partners, and ignored rural women. Then the statistical extrapolations exaggerated those errors.

Recently, the United States Agency for International Development began financing surveys that chose thousands of households at random in both urban and rural areas and sent in health care workers to take detailed medical and lifestyle histories and blood samples; though expensive, they produced results that are considered more accurate.

In July, India's estimated caseload was revised downward, to 2.5 million, from 5.7 million -- a change that accounts for about half the drop in the new Unaids figures. Officials said then that India's epidemic was not ''generalized'' -- that is, it had not spread far from the original high-risk groups like brothel workers and clients, truckers, heroin users and gay men. Also, rates among prostitutes appeared to have fallen as condoms gained acceptance. Instead of being considered the world's worst-hit country, India fell to third place behind South Africa and Nigeria.

Also, some African countries have seen real drops in new cases. It happened relatively early in Uganda, after an aggressive ''no grazing'' (meaning no casual sex) campaign started 20 years ago. Similar declines appear to have happened in Zimbabwe and Kenya, especially since people saw many friends and relatives die. Rather than embracing condoms or circumcision, people decided to have sexual relations with fewer people, Dr. Halperin said.

''You don't need a Ph.D. to figure out that if you reduce your number of partners, you reduce your risk,'' he added.

A small decline in new infections can quickly cut a country's total caseload because large numbers of people infected early in the epidemic are still dying.

AIDS advocates fear that any suggestion that the epidemic is lessening in intensity will cause fatigued donors to contribute less.

In September, for example, the Global Fund to Fight AIDS, Malaria and Tuberculosis received pledges of only $9.7 billion, well short of the $15 billion to $18 billion it had hoped to raise.

''There's still a huge epidemic out there that still needs huge resources to win the battle,'' said Paul Zeitz, executive director of the Global AIDS Alliance, a non-profit advocacy group.

Correction: November 21, 2007, Wednesday
A front-page article in some editions yesterday about lower estimates of the number of H.I.V. infections worldwide misstated a researcher's explanation for a drop in infection rates in some African countries. The researcher, Daniel Halperin of the Harvard School of Public Health, said surveys indicated that people in Kenya and Zimbabwe chose to have fewer sexual partners rather than to use condoms more often. He did not mention circumcision to prevent AIDS as a consideration in those countries.